This invention relates to antenna arrays, and more particularly to a triple-band, trap loaded antenna for GPS use.
The global positioning system (GPS) includes a constellation of satellites in low earth orbit. These satellites emits signals allowing a receiver to determine its position very accurately. The current GPS system utilizes signals in two frequency bands referred to as L1 and L2. Signals in the L1 band are centered at 1575.42 MHz and signals in the L2 band are centered at 1227.60 MHz. These signals, available for both civilian and military users, have a 20 MHz bandwidth with a proposed extension to 24 MHz to accommodate a new military M-code that will be inserted into new GPS Block IIF satellites scheduled for launch beginning in 2005. These new GPS Block IIF satellites will also carry a new signal frequency band designated as L5 and located at 1176.45 MHz with a 20 MHz bandwidth. This new signal referred to as the “safety of life” navigation signal will allow precision approach navigation on a world-wide basis and provide mitigation against interference. Thus, the modernized GPS system will require receivers responsive to all three frequency bands L1, L2 and L5. Such receivers, therefore, will require an antenna system with good gain coverage at all three frequency bands over the required bandwidth.
A known GPS antenna is a dual-frequency quadriflar helix antenna developed at the Mitre Corporation, assignee of this patent application. This antenna employs RF trap loading. See, D. P. Lamensdorf, M. Smolinski, “Dual Frequency Quadrifilar Helix Antenna” proceedings 2002, IEEE-APS International Symposium, San Antonio, Tex., Vol. 3, paper 87.5, pp. 488-491. This antenna is also the subject of a co-owned patent application, Ser. No. 10/174,330 filed Jun. 18, 2002. Trap loading has also previously been used by amateur radio operators for increasing the bandwidth of monopole and dipole antennas operating in the HF and VHF bands. See, “The ARRL Antenna Handbook,” 15th Edition, Published by The American Relay League, Newington, Conn., 1988, pp. 7-8 to 7-14.
Inverted L antennas are also known. Such antennas are compact, low profile transmission line type antennas that have been used in various forms for missiles, vehicular communication systems, and in mobile telephone systems. See, R. W. P. King, C. W. Harrison, “Transrnission Line Antennas with Application to Missiles” in “Antennas and Waves,” The MIT Press, 1969, pp. 437-481; K. Fujimoto, A. Henderson, J. R. James, “Inverted L Antennas” in “Small Antennas,” Section 2.4, John Wiley & Sons, 1987, pp. 116-151; K. Fujimoto, J. R. James, “Mobile Antenna Systems Handbook,” ARTECH House Publishers, 1994, pp. 217-228.
A trap loaded Planar Inverted F Antenna (PIFA), a variant of the inverted L antenna, has also recently been designed for operation at 900 MHz (cellular systems) and 1800 MHz (personal communication systems). See, G. H. K. Lui, R. D. Murch, “Compact Dual-Frequency PIFA Designs Using LC Resonators,” IEEE Transactions on Antennas and Propagation, Vol. 49, No. 7, July 2001, pp. 1016-1019 and A. K. Shriverik, J.-F. Zurcher, O. Staub and J. R. Mosig, “PCS Antenna Design: The Challenge of Miniaturization,” IEEE Antennas and Propagation Magazine, Vol. 43, No. 4, August 2001, pp. 22-23.